Under-Actuation Mechanism for Shadow Hand

[JYChen18]

Which model is the issue affecting?
Shadow Hand EM35

What is the issue?
The under-actuation mechanism in the MuJoCo simulation differs significantly from that of the real product, contributing to a large sim2real gap, especially in precise grasping and manipulation tasks.

In the simulation, the motion of FFJ1 and FFJ2 is always identical, with each joint receiving roughly half of the combined control signal FFJ0, mediated by the tendon. However, on the real Shadow Hand, the behavior is different: when the control signal FFJ0 is less than 90 degrees, FFJ1 remains nearly stable while FFJ2 increases. Once FFJ0 exceeds 90 degrees, FFJ1 begins to increase and FFJ2 stops moving.

Given that the real product’s behavior cannot be altered, is there a mechanism in MuJoCo that can better approximate this phenomenon to reduce the sim2real gap?

Is there any additional context you can provide (e.g., a spec sheet or a URDF to show a value mismatch)?
No.